The present invention relates to a rotary disc for a disc brake assembly arranged to be pressed at its outer peripheral portion by a pair of brake friction pads in the brake assembly.
In general, the outer peripheral portion of such a conventional rotary disc as described above has uniform mass and rigidity. For this reason, when the outer peripheral portion of the rotary disc is vibrated at one point, node and antinode positions of a vibration mode of the rotary disc are determined by the vibrated point, and these positions vary with change of the vibrated point. This means that such node and antinode positions in the vibration mode of the rotary disc are determined by the assembled position of a brake friction pad which acts to apply a vibration to the rotary disc in braking operation. In other words, there occurs a standing vibration mode with fixed nodes and antinodes on the rotary disc during braking. Such a standing vibration mode causes undesired noises at its resonant frequency. It is also noted that the same standing vibration mode does not occur in all disc brake assemblies because the undesired braking noises occur in a close relationship with the construction of the entire disc brake assembly. This means that in many cases there occur a plurality of standing vibration modes on the same disc brake assembly. For the above reasons, it is required to eliminate such occurrence of all the standing vibration modes so as to effectively decrease the braking noises in all the disc brake assemblies.